Lactic acid purification of chitin from prawn waste using a horizontal rotating bioreactor

Shellfish waste obtained from seafood processing plants contains chitin, protein and calcium carbonate. Chitin is a versatile biopolymer with many applications. Conventionally, chitin is separated from calcium carbonate and protein by acid and alkali respectively. In this project, a biotechnological approach was applied to recover chitin from scampi (Nephrops norvegicus) waste using lactic acid bacteria (LAB) to produce lactic acid from glucose which lowers the pH of the mixture, thus preserving the waste from spoilage. The acid also dissolves the calcium carbonate and under these conditions native enzymes breakdown the protein (autolysis), thus affording a substantial amount of purification of chitin. LAB were isolated and identified from various shellfish waste fermentations. Studies on their acid-producing ability revealed a few potentially good strains, identified as Lactobacillus paracasei, Lactobacillus plantarum and Pediococcus sp. The strain of Lactobacillus paracasei was used as a starter culture in the fermentation of shellfish waste in a horizontal rotating bioreactor in order to evaluate the feasibility of the process. The design of the bioreactor was such that it enabled separation of solid and liquid end products during fermentation. Several important fermentation parameters were studied including mode of rotation, concentration of glucose, temperature, rotation rates, loading capacity, type and particle size of waste. Partial purification of the scampi waste was achieved using both batch and fed batch operation, but in the latter, improved purification was achieved at the cost of increased glucose consumption and extended fermentation times. Whilst higher temperatures increased the rates of fermentation, higher rotation rates seemed to have the reverse effect. Mincing the waste helped to increase breakdown of protein whilst larger particles tended to undergo rapid spoilage. Analysis of the chitin product enabled this method to be compared with the conventional method. The results obtained showed that this method is capable of saving large volumes of chemicals and besides producing chitin, the protein liquor by-product could also be used as an ingredient in an animal feed which is not possible by the conventional method.